This application claims priority from Japanese Patent Application No. 2001-59,440 under 35 U.S.C. xc2xa7 119.
This invention relates to a scanning magnetism detector for use with a tunnel electron microscope and a probe for use with the scanning magnetism detector.
A conventional scanning magnetism detector has a probe made of a ferromagnetic metal or a single crystal of chromium dioxide. Such scanning magnetism detectors are employed to investigate the surface condition of a magnetic substance on an atomic scale through measurement of a tunnel current between the probe and the magnetic substance.
In a scanning magnetism detector having a probe composed of ferromagnetic metal, the probe may undergo strong magnetic interaction with the magnetic substance being measured. Thus, a measured magnetic condition of the magnetic substance may be distorted. This distortion can make it difficult to precisely investigate surface conditions of the magnetic substance.
On the other hand, in a scanning magnetism detector having a probe composed of a chromium dioxide single crystal, a residual magnetic condition (spin condition) at the probe tip is normally present. Furthermore, the probe tip may be contaminated because of physical properties of the oxide.
Because of these limitations, a scanning magnetism detector having a probe composed of a Group Ill-V semiconductor compound has been proposed. In a scanning magnetism detector, a tunnel current of spin-polarized conduction electrons of the Group Ill-V semiconductor compound can be used because of photoexcitation of the spin polarized electrons. Since the Group III-V semiconductor compound is non-magnetic, the above-mentioned magnetic distortion does not occur. However, such a detector will normally be large and complex because a laser system may be required.
An object of the present invention is to provide a new probe for use with a scanning magnetism detector.
The present invention relates to a scanning magnetism detector comprising a probe made of a solid material of a single crystal having spin polarization and electrical conductivity properties. The probe positioned in proximity to a magnetic substance enables detection of its surface condition by measurement of a tunnel current flowing between the probe and the surface of the magnetic substance.
The present invention also relates to a probe made and used as described above for a scanning magnetism detector.
When a probe of the scanning magnetism detector in accordance with the present invention is positioned in proximity to a surface of a given magnetic substance, a wave function of electrons in a forefront region or tip of the probe overlaps with an S-type wave function of electrons in the surface of the magnetic substance. Under these circumstances, the probe is magnetically saturated by an exchange interaction from the magnetic field of the magnetic substance and, as a consequence, a tunnel current flows between the probe and the magnetic substance. The amount and the direction of the tunnel current depend on the magnitude and the direction of the magnetic moment in the surface of the magnetic substance.
As the magnitude of the magnetic moment in the surface of the magnetic substance becomes larger, the amount of the tunnel current becomes larger. The tunnel current flows in a direction that is parallel to the direction of the magnetic moment.
If the type and the arrangement of atoms forming the surface of the magnetic substance are changed, then the magnetic moment of the magnetic substance is also changed. Therefore, the amount and the direction of the detected tunnel current depend on the type and the arrangement of the atoms constituting the surface of the magnetic substance. The surface condition of the magnetic substance can, therefore, be detected by the amount and the direction of the tunnel current.
Additional aspects and advantages of this invention will be apparent from the following detailed description of preferred embodiments thereof.